/*
 * Copyright (c) 2011-2012 Alexander Dubu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * o  Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * o  Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * o  Neither the name Axil nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package axil.stdlib.reflection.function;

import axil.api.AxilObject;
import axil.api.extend.Environment;
import axil.api.extend.Function;
import axil.api.extend.Parameters;
import axil.api.extend.Source;
import axil.engine.function.Functor;
import axil.vm.stack.StackFrame;

import static axil.framework.Functions.callable;


/**
 * This is used for dynamically invoking a function. The call() function takes
 * two arguments: the function to be invoked and a collection containing the
 * arguments to be passed. For example:
 *
 * 		call(function, list(12, 34, 56))
 *
 * The call() function is not variable argument since that would make many
 * dynamic programming problems sticky to deal with, since you could not
 * generically collect arguments and pass them as a unit.
 *
 * You can also pass a function that returns a function, if you're feeling very
 * fancy and reflective:
 *
 * 		call(lookup-func("foo"), list(4, 5, 6));
 *
 * The function always performs eager evaluation. If the function passed has
 * lazy evaluation, then it will likely not work as intended. For example,
 * passing the "if" function:
 *
 * 		call(lookup-func("if"), list(print("a"), print("b")))
 *
 * Would not print as intended, since both "a" and "b" would be printed at the
 * time the arguments are assembled. So, this would work as intended:
 *
 * 		call(lookup-func("if"), list(quote(print("a")), quote(print("b"))))
 *
 * See the quote() function for details.
 */
public class Call implements Function {
	/**
	 * Evaluate this function in the given context and environment. A non-null
	 * object must be returned. Since we are invoking a function that was passed
	 * by reference, we first get the function itself then create a stack frame
	 * that contains the passed arguments. So, this:
	 *
	 * 		call(func, a, b, c)
	 *
	 * Turns into this, effectively:
	 *
	 * 		func.call(a, b, c)
	 */
	public AxilObject eval(Environment env, Parameters params, Source source) {
		Functor func = callable(params.a());
		final int size = params.size();
		StackFrame sf = StackFrame.create(params, source, func.ids());
		for (int i = 1; i < size; i ++) {
			sf.at(i - 1, params.at(i));
		}
		return func.call(env, sf);
	}
}
